1. Field of the Invention
This invention relates to electronic circuits and more particularly to complex computer aided design layout and design rule verification of a design layout of, for example, an integrated circuit (IC) device or printed wiring board, in preparation for fabrication.
2. Description of the Related Art
Design of an electronic circuit, for example, an integrated circuit (IC), is a complicated and time consuming process. FIG. 1 illustrates a typical design flow 100 of an integrated circuit device from conception through the generation of a fabrication ready design layout. Generally, design flow 100 commences with defining the design specifications or requirements, such as required functionality and timing, step 102. The requirements of the design are implemented, for example, as a net-list or electronic circuit description, step 104. The implementation can be performed by, for example, schematic capture (drawing the design with a computer aided design tool) or more typically, utilizing a high level description language such as VHDL, Verilog and the like. The implemented design is simulated to verify design accuracy, step 106. Design implementation and simulation are iterative processes. For example, errors found by simulation are corrected by design implementation and re-simulated.
Once the design is verified for accuracy with simulation, a design layout of the design is created, step 108. The design layout describes the detailed design geometries and the relative positioning of each design layer to be used in actual fabrication. The design layout is very tightly linked to overall circuit performance (area, speed and power dissipation) because the physical structure defined by the design layout determines, for example, the transconductances of the transistors, the parasitic capacitances and resistances, and the silicon area which is used to realize a certain function. The detailed design layout requires a very intensive and time-consuming design effort and is typically performed utilizing specialized computer aided design (CAD) or Electronic Design Automation (EDA) tools.
The design layout is checked against a set of design rules in a design rule check (DRC), step 110. The created design layout must conform to a complex set of design rules in order, for example, to ensure a lower probability of fabrication defects. The design rules specify, for example, how far apart various layers must be, or how large or small various aspects of the layout must be for successful fabrication, given the tolerances and other limitations of the fabrication process. A design rule can be, for example, a minimum spacing amount between geometries and is typically closely associated to the technology, fabrication process and design characteristics. For example, different minimum spacing amounts between geometries can be specified for different sizes of geometries. DRC is a time-consuming iterative process that often requires manual manipulation and interaction by the designer. The designer performs design layout and DRC iteratively, reshaping and moving design geometries to correct all layout errors and achieve a DRC clean (violation free) design.
Circuit extraction is performed after the design layout is completed and error free, step 112. The extracted circuit identifies individual transistors and interconnections, for example, on various layers, as well as the parasitic resistances and capacitances present between the layers. A layout versus schematic check (LVS) is performed, step 114, where the extracted net-list is compared to the design implementation created in step 104. LVS ensures that the design layout is a correct realization of the intended circuit topology. Any errors such as unintended connections between transistors, or missing connections/devices, etc. must be corrected in the design layout before proceeding to post-layout simulation, step 116. The post-layout simulation is performed using the extracted net-list which provides a clear assessment of the circuit speed, the influence of circuit parasitics (such as parasitic capacitances and resistances), and any glitches that can occur due to signal delay mismatches. Once post-layout simulation is complete and all errors found by DRC are corrected, the design is ready for fabrication and is sent to a fabrication facility.
As electronic circuit densities increase and technology advances, for example, in deep sub-micron circuits, skilled designers attempt to maximize the utilization of the design layout and manufacturability and reliability of the circuit. For example, the density can be increased, redundant vias added, and the like. Creation of a design layout and performing DRC become critical time consuming processes. Performing a DRC and manipulation of the design layout often requires manual interaction from the designer. A reliable, automated technique for improving the design layout is needed.
Accordingly, it has been discovered that automated techniques to correct certain rule violations with respect to non-design geometries can be used, simplifying and automating the design layout of an electronic circuit, whether embodied as a design encoding or as a fabricated electronic circuit.
Accordingly, in one embodiment, correcting minimum spacing rule violations is accomplished by enlarging a design geometry at erroneous boundaries toward one or more non-virtual boundaries of a wide class object of a non-design geometry avoiding one or more shielding areas around one or more virtual edges of the wide class object of the non-design geometry creating an enlarged design geometry; and deducting the enlarged design geometry from the non-design geometry.
In another embodiment, the enlarging is accomplished by creating the one or more shielding areas adjacent to the one or more virtual edges of the wide class object of the non-design geometry; and stretching and sizing outward erroneous edges of the design geometry avoiding the one or more shielding areas to create one or more cutting areas on the non-design geometry.
In another embodiment, creating the one or more shielding areas is accomplished by sizing each virtual edge not touching a virtual convex vertex outward by a minimum spacing rule amount; stretching ends of other virtual edges touching a virtual convex vertex by the minimum spacing rule amount forming stretched edges; and sizing the stretched edges by the minimum spacing rule amount.
In another embodiment, stretching and sizing outward the erroneous edges of the design geometry is accomplished by identifying the erroneous edges of the design geometry that violate a minimum spacing rule with respect to non-virtual edges of the wide class object of the non-design geometry; stretching the erroneous edges in both directions by the minimum spacing rule amount creating stretched erroneous edges; and sizing portions of the stretched erroneous edges which are not in shielding areas, which are abutting the erroneous edges, and which are not interior to the design geometry outward by the minimum spacing rule amount.
In another embodiment, the enlarging is accomplished by stretching non-virtual edges forming a non-virtual convex vertex of the one or more wide class objects of the non-design geometry by a minimum spacing rule amount to create a touching box; identifying one or more convex vertices of the design geometry inside the touching box; stretching edges forming the one or more convex vertices of the design geometry by the minimum spacing rule amount to create stretched vertex edges; sizing the stretched vertex edges to create one or more corner to corner cutting boxes; and deducting the corner to corner cutting boxes from the non-design geometry.
In another embodiment, the design geometry is a feature on a metal layer of a design layout.
In another embodiment, the non-design geometry is a dummy geometry.
The foregoing is a summary and thus contains, by necessity, simplifications, generalizations and omissions of detail; consequently, those skilled in the art will appreciate that the summary is illustrative only and is not intended to be in any way limiting. As will also be apparent to one of skill in the art, the operations disclosed herein may be implemented in a number of ways, and such changes and modifications may be made without departing from this invention and its broader aspects. Other aspects, inventive features, and advantages of the present invention, as defined solely by the claims, will become apparent in the non-limiting detailed description set forth below.